Steam turbine plants are usually dimensioned from economic points of view. Particularly in the case of steam turbine plants which are used in electric power generation, operation is carried out with very large power units for achieving the highest levels of efficiency. The efficiency, moreover, is to be constant over an operating range which is as wide as possible. To this end, it is known to feed inlet steam, especially a low-pressure inlet steam, into an intermediate-pressure steam turbine or low-pressure steam turbine. If the steam turbine is run in partial load operation, for example, the inlet steam has to be throttled at the feed point, providing this is made available at constant pressure.
In combined gas and steam turbine plants, steam is produced for a plurality of pressure stages, for example live steam, intermediate-pressure inlet steam and low-pressure inlet steam during a triple pressure process. In this case, a fuel with high sulfur content is frequently used. In this case, it may be necessary to increase the pressure of the low-pressure inlet steam in order to prevent sulfurous acid condensing out on the heat transfer surfaces of a steam generator on account of the high sulfur content of the fuel. In return, the low-pressure inlet steam needs to be correspondingly throttled at the feed point. It is disadvantageous in this case that energy is consumed with the throttling of the inlet steam, that is to say the capability of the steam to perform work in the cyclic process reduces, as a result of which the efficiency of the overall steam power process falls.